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How long a time period before a mains off and on is better than going to standy?

Discussion in 'Amps and Cabs [BG]' started by Jim C, Apr 4, 2009.


  1. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Dear Talkbass,
    Sometimes when working from home I'll take breaks and practice through my SVT. It's a no brainer that if it's less than an hour between sessions, one would go to standy.

    But what if you go out for a few hours?
    Better for the tubes to idle in standy, or, go through the power down / power up cycle for more playing?
    Is there any suggested max duration in standy?

    Did a search but no info found.

    Also, after a gig and before shut down, some threads say that leaving the amp in standby before killing the mains does not help with the cooling of tubes.
    Does the fan help with cooling when the heaters are on in standby or is this just a waste of time?

    Sincerely,
    Valve Respector in MD
     
  2. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Leaving an amplifier on standby for extended period of time will lead to cathode stripping. Standby should be used for short periods of time only.

    Turn the power off with the standby on will allow the tubes to drain the power supply.

    Paul
     
  3. Agreed, turn it off. Standby is just to turn the amp off while it's still in use (Waiting for the drummer to finish soundchecking....)

    If your leaving the amp... turn it off!

    As for after gig's, I have just slipped into the habit of putting it on standby then then turning the amp off after i have unplugged n all that.

    Also, putting the master volume to zero, don't want them pops!
     
  4. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    So turning on and off is not that bad a thing?
    How about between sets if there is a 15 or 20 minute break?

    I've left this amp on in standby for hours at a time.
    Looks like it might be time to do some tube testing.
     
  5. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    That sort of time frame should give you no trouble it's the hours that lead to problems.

    Paul
     
  6. A) How do you strip cathode emissive material with no electron flow (in standby).
    B) How is it better to cycle a heater on and off (extreme stress on heaters).
    C) When electron flow stops (amp in standby) tubes do not conduct (other than the heaters) so how can they drain a powersupply in a non-conducting state.
    D) Who stole BassmanPaul's login? :)

    Jon
     
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Unfortunately having a hot cathode emits electrons and, as there is no current flow in the tube, there is nothing to replace them. Similarly when a tube has plate voltage and a cold heater, again electrons are drawn from the cathode. One of the reasons amps got fitted with standby switches in the first place. Amps with tube rectifiers did not suffer from this as the B+ was applied after the tubes had warmed up.

    When I said the supply is drained I meant the standby switch has to be on not off. While it's on and the power is off, the residual heat in the heater allows current to flow until the supply caps are drained. Try playing and have someone switch the ac off. The amp will continue to play for a short while. The longer this is the better the supply caps are.

    Paul
     
  8. MIJ-VI

    MIJ-VI Banned Supporting Member

    Jan 12, 2009
    Ampeg SVT: 'Practice Amp'. :hyper: :)
     
  9. Dogbertday

    Dogbertday Commercial User

    Jul 10, 2007
    SE Wisconsin
    Blaine Music LLC
    If I had one I'd practice through it
     
  10. MIJ-VI

    MIJ-VI Banned Supporting Member

    Jan 12, 2009
    I did. And I did! :hyper:
     
  11. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Why practice through an SVT; because I can.
    The practice and combo amps sit in the corner in utter confusion.

    So, bottom line:
    * Leaving the amp in standby vs. on position does not extend tube life
    * Standby before shut off does not help cool the tubes
    * When the power switch is on, the clock is running as far as tube life
    * If you are not going to play for say an hour, kill the mains

    Is this correct?
     
  12. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Pretty much.

    Paul
     
  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The cathode stripping deal..... well..... Ok. The problem is not so much the electrons that leave the cathode, it is that they come back again. When voltage is on the tube, they leave and go to the plate or screen..... but if there is no electric field to take them away*, they will come back and their impacts over time can damage the electron emitting coating.

    it is fairly theoretical for most usage, but leaving the heaters on for hours routinely is not "most usage".

    I will agree that standby is perfect for breaks...... when you come back, nobody wants to stand around waiting for things to warm up.

    if you will be not using the amp for some longer time, just turn it off.

    * for the extreme techie types.... yes, the "space charge" can actually repel them back into the cathode after they are thermally ejected.
     
  14. I will site a Motorolla study done in the wainning days of tube color TV's in that the instant on feature resulted in a < 2% decrease in emmision from a 5 hour on, 19 hour "standby" (heaters on only) attributed to cathode poisoning after almost one year of service.
    Of course that was in the days of superior tube production. Yes I worked for a repair shop in high school, we had movies that were talkies also :p The correct term for standby issues is "cathode poisoning" not "cathode stripping". Cathode stripping happens to cold cathodes when you apply high voltage without warm up. :)
     
  15. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I was trying to simplify a fairly complex subject into something more understandable to the less technically minded.

    Paul
     
  16. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I too switched tube amps on with the standby on for many years. Some tube amps never even came with standby switches. My view is that you should not obsess over this too much. You may have shortened tube life but as the Motorola study you cited says the difference will not be catastrophic or probably even noticeable!

    Paul
     
  17. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Thanks very much; really appreciate all of your efforts.

    Last question:
    I assume that this mostly applies to power tubes.
    I worked for 3 large studios back in the day and the head techs always had us leave all the gear on 24/7 including the tube Pultec EQ's and Urei limiters. We did turn off the Telefunken and Neuman tube mics but that was so they could be put away to keep dust off the capsules. We did use the rack gear most of the time (morning session were 10:00-6:00 and night session 7:30-3:30 : 5 days per week)
    So, for high use pre-amps would you leave them on, or cycle off when not in use?
    The techs were defineately not trained in tube gear.

    The studys done for studios always showed much high failure rate for discrete and digital gear when turned on and off daily but never mentioned tube gear.
     

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